Device for the dosing of a reducing agent

ABSTRACT

An apparatus for metering a urea or a urea-water solution for delivery to a catalytic converter assembly for removing nitrogen oxides from the exhaust gases of a Diesel engine, includes a housing block supporting function components communicating via a line, formed by recesses in the housing block, for transporting the reducing agent, and the walls of the line are formed by the housing block. This apparatus assures a simple line layout for reducing agent with a minimum number of sealing points that is accordingly appropriate for large-scale mass production.

PRIOR ART

The invention is based on an apparatus for metering a reducing agent, inparticular a urea or a urea-water solution, in the context of catalyticposttreatment of exhaust gases, as generically defined by the preambleto the main claim.

To achieve a reduction in NO_(x) components in exhaust gases, reductioncatalytic converters have been developed, especially for Diesel engines,and are typically classified as either so-called SCR catalyticconverters (for Selective Catalytic Reduction) or reservoir-typecatalytic converters. The so-called SCR catalytic converters areregenerated by delivering a reducing agent comprising urea and/orammonia, while the so-called reservoir-type catalytic converters areregenerated in so-called rich exhaust gas phases with hydrocarbons fromthe entrained internal combustion engine fuel.

It is known for the various components of a metering system to be madeto communicate via hoses. From German Patent Application 199 46 900.8,an apparatus is known which for removing nitrogen oxides from exhaustgases, for instance from a Diesel engine, meters in urea as a reducingagent. Means intended for this purpose are sometimes secured to aplastic or metal block or integrated with such a block. The meteringsystem described is relatively large and complicated to produce, sinceit comprises a plurality of components located in line with one another.

ADVANTAGES OF THE INVENTION

The metering apparatus of the invention, having the characteristics ofthe body of the main claim, has the advantage over the prior art of asimple, sturdy line layout with a minimum number of sealing points,which can be produced economically and in large-scale mass production.Since there are only a few sealing points, there is less risk of leaksand therefore less risk of failure. Hoses and separate screw fasteningsfor lines can be omitted. Because of the smaller number of requiredcomponents and the smaller structural size, the effort and expense ofassembly is less, the overall structural volume is decreased, and theproduction and system costs are thus lowered. The structural unit can bechecked for tightness, for instance, after preassembly, which meansreduced rejection costs compared to finding defects upon final systemchecking. The recesses can be disposed in various ways, for instance inthe form of bores; additional bores make it possible to expand the basicfunctions of the metering apparatus by mounting additional components.The provision of recesses in a housing block makes it possible to attachthe metering means and other function components to the housing block;the length of the line filled with reducing agent is kept short as aresult, so that the liquid can be rapidly thawed again after ice forms.Short line layouts are also fast to fill, and the requisite pressure foroperation can be built up quickly.

By the provisions recited in the dependent claims, advantageousrefinements of and improvements to the metering apparatus defined by themain claim are possible. It is especially advantageous for all the meansto be connected to one another via at least one rectilinear supply linethat traverses the entire housing block. This line layout is simple toproduce and makes possible an adroit arrangement of components that haveto be connected to one another. Moreover, it can be embodied in a simpleway as an injection-molded bore, for instance in a plastic block thatreceives the various system components.

The open ends of the line can advantageously be closed by functioncomponents, so that separate closure elements such as closure screws areunnecessary.

A heating element, introduced in particular axially parallel to therecess, such as an electric heating rod embodied as an electricalresistor, can advantageously heat a central line quickly in order tothaw a frozen fluid or to protect the apparatus from freezing.Alternatively, or in combination with the electric heating rod, thehousing block can also comprise an electrically conductive material, inparticular an electrically conductive plastic, which as described inGerman Patent Application 199 46 900.8, is provided with electrodes thatcan be subjected to an electrical voltage, in order to achieve anelectric current for heating the entire assembly by way of the housingblock.

The material comprising the housing block is advantageously selectedsuch that because of a low modulus of elasticity of the material, thismaterial can contribute to volumetric compensation if ice forms in theline.

It is also advantageous to integrate compensatory or resilient elementsin the assembly, so that a freezing-resistant metering system can befurnished that remains intact after freezing and thawing cycles and thatprotects integrated components against destruction from ice formation.The individual components themselves need not be embodied as completelyfreeze-resistant. Moreover, materials that are not resistant to highpressure can also be used, in particular for the housing block, sincethe buildup of excessive pressure forces in such extreme situations asfreezing is averted.

DRAWING

Exemplary embodiments of the invention are shown in the drawing andexplained in further detail in the ensuing description. Shown are

FIG. 1, the functional layout of a metering apparatus;

FIG. 2, components of a metering apparatus that are integrated into ahousing block provided with recesses;

FIG. 3, the detail view of a further embodiment of the invention; and

FIG. 4, a further detail view.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In FIG. 1, reference numeral 1 indicates the inlet to the meteringapparatus, by way of which a urea-water solution is supplied to theapparatus. A metering pump 4 aspirates the fluid. The pump 4 isrpm-controlled via a stepping motor 4 a. A pressure regulator 11 carriesany excess pumped quantity of fluid via the outlet 11 a of the pressureregulator either back to the inlet of the metering apparatus or to themetering pump or to a urea tank, not shown in detail, from which themetering pump 4 is supplied via the inlet 1. The line 12 connecting theinlet 1, pump 4 and pressure regulator 11 carries the pumped fluidonward to a metering valve 7. A pressure sensor 50 for measuring thepressure in the line 12 is mounted upstream of the metering valve. Themetering valve is electrically triggerable and dispenses the fluid inaccordance with the electrical triggering to components connected to theoutlet 14. This is for example a mixing chamber, not shown in detail butalready described in the aforementioned German application 199 46 900.8,to which compressed air from a compressed air container can be deliveredin order to form an aerosol from the urea-water solution, which can thenbe injected into the inlet region, in particular of a motor vehicleexhaust gas catalytic converter.

The metering pump 4 meters the requisite quantity of urea-water solutionin accordance with the reducing method employed. A control unit, notshown in detail, acquires data for this purpose pertaining to the engineoperating state, which are received from a higher-ranking engine controlunit via a CAN data line, along with the signals of various pressure,temperature and fill level sensors, not described in detail here.

From the sensor information and the information from the engine controlunit, the control unit calculates a urea metering quantity and triggersthe metering valve accordingly.

In an alternative embodiment, the reducing agent can also be injected bythe injection valve 7 directly into the inlet region of the catalyticconverter, in other words without reinforcement with compressed air orwithout having to provide a mixing chamber.

FIG. 2 is a cross-sectional view through a metering apparatus of theinvention, which has a housing block 400, in particular of electricallyconductive plastic, with a modulus of elasticity between approximately1000 N/mm² and approximately 7000 N/mm². The housing block has recessesin the form of bores 80, 81, 82 and 83, which form the reducing agentline 12 shown in FIG. 1. The bore 80 traverses the entire block. Thepump lines 60 of the metering pump 40 are connected via O-rings to theends of the bores 80 and 82, and the pump is secured to the surface ofthe housing block via an elastic sheet-metal angle piece 61. A pressureregulator 11, acting to compensate for pressure if ice forms and havinga diaphragm not shown in detail, is flanged to the surface of thehousing block, and two O-rings seal off the head of the pressureregulator that protrudes into the housing block. Analogously, a meteringvalve 7 is secured to the housing block. On the end of the housing blockopposite the metering pump 4, the bore 80 merges with a region of largercross section, where a pressure sensor 50 is accommodated. The pressuresensor is secured to the surface of the housing block via a flexible,elastic flange 51. Once again, O-rings assure sealing of the bore thatcan be filled with a fluid.

Via the bore 81, the metering valve 7 communicates with the flanged-onoutlet 140 of the metering apparatus. The inlet 1 flanged on next to itcommunicates with the bores 83 and 82 and serves to supply the reducingagent from a reservoir to the metering pump 4. In the bore 80, betweenthe pressure regulator 11 and the metering valve 7, there is anair-filled elastic hose 63, which is secured to the bore wall, forinstance by means of an adhesive. The electric pump motor, which is alsosecured to the housing block 400, is disposed above the metering pump. Acontrol unit, not shown in detail, is connected electrically, in amanner not shown in detail, to both the metering valve and the pressuresensor and also to other sensors, not shown in detail, such as a filllevel sensor for the urea tank, and from the engine control unit thiscontrol unit receives data on the operating state of the engine whoseexhaust gases are to be chemically reduced with the aid of the meteringapparatus in the exhaust system.

The housing block 400 serves to receive and secure various means forsupply reducing agent and further function components, such as thepressure sensor 50, metering valve 7, pressure regulator 11 and meteringpump 4. The rectilinear bore 80 traverses the housing block from one endto the other and can be designed in a way appropriate for manufacture,for instance conically or stepped in the case of a plastic block, orcylindrically for the sake of metal-cutting machining in the case of ametal housing block. In addition, further bores 81 through 83 areprovided, some of which extend parallel and others perpendicular to thethrough bore 80 and assure the attachment of the assembly to a reducingagent reservoir and to the catalytic converter as well as assuringpressure compensation via the pressure regulator 11. The pressureregulator 11 and the metering valve 7 protrude with their lineconnections, not visible in the drawings, into the bore 80, so that theyeach communicate with the bore; simultaneously, they close off the borefrom the outside. The assembly has a plurality of structuralcharacteristics for compensating for volumetric fluctuations resultingfrom freezing or melting of the reducing agent during cold weather.Because the metering pump 4 is secured to the housing block 400 by meansof the elastic sheet-metal angle piece 61, a compensation capability inthe event of severe pressure fluctuations caused by a phase transitionis assured because the pump lines 60 together with the metering pump 4all move relative to the bores 80 and 82, and thus the volume in theline system that carries the reducing agent can adapt automatically whenotherwise the housing block could burst, or such components as themetering valve or pressure sensor could become damaged. O-ring sealscontinue to keep the line tightly closed. The pressure sensor 50,secured axially resiliently to the housing block via the flexibleelastic flange 51, is likewise pressed outward by a volumetric expansionin the event of ice formation. If the ice melts again, the pressuresensor and the metering pump move reversibly back to their outsetposition. The pressure regulator 11, which is known per se and iscommercially available, has a built-in elastic diaphragm, which isrelieved to the ambient air. This diaphragm can yield elastically if iceforms and can thus also help to compensate for the increase in volume ifice forms. Moreover, because of its low modulus of elasticity, thehousing block can to a certain extent absorb the ice pressure byexpanding. In addition, the air-filled elastic hose 63 serves to reducethe circumferential tension in the bore wall, because upon freezing of aurea-water solution, for instance, it is compressed and thus can absorbsome of the line pressure building up at the time.

In an alternative embodiment, still other bores may be provided, whichconnect the components for feeding and metering compressed air to oneanother, so that if a compressed air-supported development of an aerosolis intended for injection into a catalytic converter assembly, onceagain a compact, integrated assembly can be furnished. In that case,instead of the metering valve 7, a metering valve together with a mixingchamber is secured to the housing block, into which chamber the meteringvalve can be metered and which chamber can be subjected to compressedair. In this case, the outlet 140 forms the outlet of the mixingchamber. The bores both for the reducing agent lines and for the supplyof compressed air can also be made by injection molding, especially whenplastic is used.

Instead of an air-filled elastic hose 63, other volumetrically elasticelements can be used, such as gas-filled plastic microballoons; hollow,gas-filled fibers closed on the ends; or gas-filled hoses, woundspirally in a manner similar to a compression spring.

FIG. 3, in cross section, shows a detail of an alternative meteringapparatus, in which a bore discharging into a cavern 100 is provided.This bore is for instance a bore that is in communication with the bore80 via a corner connection. The cavern is embodied as a bore that isconical toward the outside and is closed with a flange 110; O-ring sealsassure sealing even if the position of the flange changes. The flange isin fact supported axially movably via compression springs 111 and screws112.

In the event of freezing, the fluid in the line, that is, in the boresand thus also in the bore discharging into the cavern 100, expands andpresses against the housing block. To a limited extent, the bore wallsyield, as already noted above. Any further increase in the pressurecould cause the housing to burst. The support of the flange 110 embodiedas a resilient element is now dimensioned such that in good time beforeany risk of bursting, it yields to the ice pressure by moving axiallyand thus limits the pressure in the bore in the event of ice formation.The conical embodiment of the bore here results in an amplified axialdirection of action of the ice pressure and carries this pressure to theresilient flange. Given suitable dimensioning of the components, thisprocess can be repeated cyclically as often as desired.

The cavern 100 can also be embodied as a cylinder, or as a cylinder witha multiply graduated inside diameter, or in other words can be formed bythe peripheral region of the bore itself or by a cylindrical hollowchamber with a different diameter, in particular a larger diameter, thanthe bore. The cavern can also have any feasible geometry.

FIG. 4 illustrates an alternative, axially movable securing of thepressure sensor 50. A compression spring 120 presses it against a borestep 131 of the sensor bore 130. The compression spring 120 is bracedhere on a threaded ring 121 that is secured to the housing block 400. AnO-ring seal 140 in a radial indentation in the pressure sensor assuressealing off of the fluid volume formed by the bore 80 and the sensorbore 130.

If the urea-water solution freezes, then as a consequence of avolumetric expansion the pressure in the bore 80 and in thewidened-diameter sensor bore 130 increases, until the spring force ofthe compression spring 120 is reached. Then the pressure sensor 50 isdisplaced counter to the spring force and increases the volume in thesensor bore 130. By this variant installation, both the pressure sensor50 and the block 400 are protected against excessively high ice pressureloads.

1-14. (Canceled)
 15. An apparatus for metering a reducing agent, inparticular urea or a urea-water solution, comprising a housing block,means (4, 7, 11), secured to the housing block for delivering thereducing agent to a catalytic converter assembly (30) for removingnitrogen oxides from the exhaust gases of a Diesel engine, said meanscommunicating via a line (12; 80, 81, 82, 83), formed by recesses in thehousing block (400), for transporting the reducing agent, and the wallsof the line (12) being formed by the housing block.
 16. The apparatus ofclaim 15, wherein at least one recess (80) rectilinearly traverses theentire housing block (400).
 17. The apparatus of claim 15, furthercomprising a heating element extending generally parallel to at leastone recess, said heating element being secured to the housing block orembedded in the housing block.
 18. The apparatus of claim 16, furthercomprising a heating element extending generally parallel to at leastone recess, said heating element being secured to the housing block orembedded in the housing block.
 19. The apparatus of claim 15, whereinthe recesses are embodied as bores.
 20. The apparatus of claim 17,wherein the recesses are embodied as bores.
 21. The apparatus of claim19, wherein the housing block is injection-molded.
 22. The apparatus ofclaim 15, wherein the housing block is of plastic.
 23. The apparatus ofclaim 22, wherein the plastic has a low modulus of elasticity in therange from approximately 1000 N/mm² to approximately 7000 N/mm².
 24. Theapparatus of claim 15, wherein all the ends of the line (12) communicatewith the means (4, 7, 11) and further function components (1, 14, 50,110), so that no separate closure elements are required.
 25. Theapparatus of claim 21, wherein all the ends of the line (12) communicatewith the means (4, 7, 11) and further function components (1, 14, 50,110), so that no separate closure elements are required.
 26. Theapparatus of claim 15, wherein one end of the line (12) is closed by acompensation element embodied as a spring-loaded flange (110).
 27. Theapparatus of claim 24, wherein one end of the line (12) is closed by acompensation element embodied as a spring-loaded flange (110).
 28. Theapparatus of claim 15, wherein the means or further function componentsare at least in part secured to the housing and connected to the line(12) with the aid of elastic elements (61, 51) in such a way that theapplicable means or function components can execute a compensatorymotion if ice forms in the line.
 29. The apparatus of claim 26, whereinthe means or further function components are at least in part secured tothe housing and connected to the line (12) with the aid of elasticelements (61, 51) in such a way that the applicable means or functioncomponents can execute a compensatory motion if ice forms in the line.30. The apparatus of claim 28, wherein said means includes a pump (4),and wherein the elastic element that secures the pump is embodied as anelastic sheet-metal angle piece (61) secured to the housing block. 31.The apparatus of claim 28, wherein the function components include apressure sensor (50), which is secured resiliently to the housing andcloses the line (12) in a tightly displaceable manner.
 32. The apparatusof claim 15, wherein means include a pressure regulator (11) that has adiaphragm acting to compensate for pressure in the event of iceformation.
 33. The apparatus of claim 15, wherein at least onevolumetrically elastic component, in particular an air-filled element(63), is disposed in the line.